High density connector and method of manufacture

Description

[0001] The present invention relates to an electrical high density connector to be mounted onto the surface of a substrate having a conductive element.

[0002] The drive to reduce the size of electronic equipment, particularly personal portable devices, and to add additional functions to such equipment, has resulted in an ongoing drive for miniaturization of all components, especially electrical connectors. Efforts to miniaturize connectors have included reducing the pitch between terminals in single or double row linear connectors, so that a relatively high number of I/O or other lines can be interconnected by connectors that fit within tightly circumscribed areas on the circuit substrates allotted for receiving connectors. The drive for miniaturization has also been accompanied by a shift in preference to surface mount techniques (SMT) for mounting components on circuit boards. The confluence of the increasing use of SMT and the required fine pitch of linear connectors has resulted in approaching the limits of SMT for high volume, low cost operations. Reducing the pitch of the terminals increases the risk of bridging adjacent solder pads or terminals during reflow of the solder paste. To satisfy the need for increased I/O density, array connectors have been proposed. Such connectors have a two dimensional array of terminals mounted on an insulative substrate and can provide improved density. However, these connectors present certain difficulties with respect to attachment to the circuit substrates by SMT techniques because the surface mount tails of most, if not all, of the terminals must be beneath the connector body. As a result, the mounting techniques used must be highly reliable because it is difficult to visually inspect the solder connections or repair them, if faulty. In the mounting of an integrated circuit (IC) on a plastic or ceramic substrate the use of ball grid array (BGA) and other similar packages has become common. In a BGA package, spherical solder balls attached to the IC package are positioned on electrical contact pads of a circuit substrate to which a layer of solder paste has been applied, typically by use of a screen or mask. The unit is then heated to a temperature at which the solder paste and at least a portion or all of the solder balls melt and fuse to an underlying conductive pad formed on the circuit substrate. The IC is thereby connected to the substrate without need of external leads on the IC. In many recent patents efforts for miniaturization of products using a SMT technology appear.

[0003] The patent application WO 98/ 15990 discloses a Ball Grid Array (BGA) technology applied to a low profile board-to-board connector system where only the reduction of the height of the assembly is required. In this purpose, contacts and solder elements are designed to be the most compact as possible.

[0004] WO 97/20454 discloses a high density connector able to connect an electronic package comprising solder element and a circuit board in which the contact includes a surface mount section having a convex bottom surface with a shape which simulates at least a lower portion of a sphere and which mimics a solder ball.

[0005] US-A-5 593 322 relates to a high density connector having fuse ball contacts located at the surface of the bottom of a male connector to connect a component to the surface of a PCB according to the well known BGA technology in which plastic supports provided on their four surfaces with metal strips are connected to a pad located at the bottom of the surface of the insulating body. Then the connector is solded to the PCB by means of a solder ball attached to the pads.

[0006] It is also known from US-A-4 767 344 that an electrical connection can be carried out by a body of reflowable material. However, as an amount of solder encircles the pin contact and envelops a predetermined region along the length of the pin this process is not applicable to a high density (with a small pitch between the rows and the columns) connector of the surface mounted type.

[0007] Patent application WO 96/42123 filed by the same applicant discloses components using contacts with a lower section comprising a bent terminal tab where the fusible material is applied to the bent surface of the tabs.

[0008] EP 0 591 772 A1 teaches another way to solder connectors to a multi layers PCB using contact pads. However, this teaching is limited to components without contacts located in an insulation housing.

[0009] US-A-5 495 668 teaches the use of links between a semi conductor chip and a printed circuit board. Links are performed by means of wires provided at their ends with solder bumps. Once again, the components are not located in an insulation housing and no contact blades are provided for further interlocking connection with a counter connector.

[0010] US-A-5 131 871 relates to a design able to reduce the stress in a connector block in a high density connector. As the walls specifying an aperture are thin the invention offers to strengthen it by using projections. These projections provide supporting means for a contact but don't secure the contact by deformation.

[0011] US-A-5 358 417 teaches a power connector using an insulative body through which a plurality of cables extend. The contact of the end of these cables occurs onto a pad and wires of these cables are mated by a conductive gel able to maintain wires and pad in abutment without solder balls.

[0012] EP 0 782 220 A2 relates to gripping means provided within apertures located in a body. Gripping means are performed by latches acting on conductive cables of ribbon cables.

[0013] Other patents were applied for inventions made to limit the wicking effect during the welding process. For example WO 97/45896 teaches a small connector for mobile phone where the length of the contact is short between its two ends. As one of the ends is dedicated to be the surface receiving the solder for surface mount process, one portion of this contact has only a nickel plating to prevent solder wicking.

[0014] US-A-3 864 004 discloses a circuit board socket with a portion of the spring contact coated with a solder resist coating in order to assure that any molten solder wicking does not flow up onto spring.

[0015] DE-PS 3 712 691 teaches also a coated electrical pin comprising an intermediate nickel layer acting as anti-diffusion barrier.

[0016] US-A-5 453 017 discloses the use of a layer of non-solderable material as coating such that solder doesn't adhere to longitudinal side.

[0017] While the use of BGA and similar systems in connecting an IC to a substrate has many advantages, a corresponding means for mounting an electrical connector or similar component on a printed wiring board (PWB) or other substrate has yet to be developed. It is important for most situations that the substrate-engaging surfaces of the solder balls are coplanar to form a substantially flat mounting interface, so that in the final application the balls will reflow and solder evenly to a planar printed circuit board substrate. Any significant differences in solder coplanarity on a given substrate can cause poor soldering performance when the connector is reflowed onto a printed circuit board. To achieve high soldering reliability, users specify very tight coplanarity requirements, usually on the order of 0.1 mm (0.004 inch). Coplanarity of the solder balls is influenced by the size of the solder ball and its positioning on the connector. The final size of the ball is dependent on the total volume of solder initially available in both the solder paste and the solder balls. In applying solder balls to a connector contact, this consideration presents particular challenges because variations in the volume of the connector contact received within the solder mass affect the potential variability of the size of the solder mass and therefore the coplanarity of the solder balls on the connector along the mounting interface.

[0018] Another problem presented in soldering connectors to a substrate is that connectors often have insulative housings which have relatively complex shapes, for example, ones having numerous cavities. Residual stresses in such thermoplastic housings can result from the molding process, from the build up of stress as a result of contact insertion or a combination of both. These housings may become warped or twisted either initially or upon heating to temperatures necessary in SMT processes, such as temperatures necessary to reflow the solder balls.

[0019] Such warping or twisting of the housing can cause a dimensional mismatch between the connector assembly and the PWB, resulting in unreliable soldering because the surface mounting elements, such as solder balls, are not sufficiently in contact with the solder paste or close to the PWB prior to soldering.

[0020] A need, therefore, exists for reliably and efficiently mounting high density electrical connectors on substrates by surface mounting techniques.

Summary of the Invention

[0021] Electrical connectors according to the present invention provide high I/O density and reliable attachment to circuit substrates by SMT techniques. These connectors exhibit high coplanarity along the mounting interface.

[0022] Electrical connectors of the present invention have the features of claim 1 and are ones in which one or more terminals are connectable by a fusible electrically conductive material to a substrate. This fusible electrically conductive material is a solder mass, preferably comprising a solder ball that can be reflowed to provide the primary electrical current path between the terminal and a circuit substrate.

[0023] Coplanarity of the surface mounting interface of the connector is maintained by providing an insulative connector housing in which stress buildup is avoided. According to this aspect of the invention, a contact terminal is inserted into an opening in the housing. The cross section of the opening is configured so that at least one side thereof has or comprises a shaped projection adapted to be deformed by the terminals as the terminal is inserted into the opening.

[0024] By means of this arrangement, stress build up as a result of multiple contact insertions is avoided, so as to minimize warping and twisting of the housing.

Brief Description of the Drawings

[0025] The connector of the present invention is further described with reference to the accompanying drawings in which:

Fig. 1 is a top plan view of a receptacle connector of a preferred embodiment of the connector of the present invention;

Fig. 2 is a partially cut away end view of the receptacle shown in Fig. 1;

Fig. 3 is a top plan view of a plug element of a preferred embodiment of the present invention;

Fig. 4 is a partially cut away end view of the plug element shown in Fig. 3;

Fig. 5 is a cut away end view of the receptacle and plug shown in Figs. 1 - 4 in unmated relation;

Fig. 6 is an end view of the receptacle and plug shown in Fig. 5 in mated relation;

Figs. 7a, 7b and 7c are cut away end views showing respectively first, second and third sequential stages in the mating of the receptacle end plug shown in Fig. 5;

Fig. 8 is a bottom plan view of the receptacle shown in Fig. 1 before the placement of solder balls thereon;

Fig. 9 is a bottom plan view of the receptacle shown in Fig. 8 after placement of the solder balls thereon;

Fig. 10 is a detailed cut away view of area XII in Fig. 1;

Fig. 11 is an enlarged view of the cut away area in Fig. 4;

Fig. 12 is an enlarged view of a cut through the cut away area in Fig. 10;

Fig. 13 is an enlarged cross sectional view through XIII-XIII in Fig. 1;

Fig. 14 is a view similar to Fig. 10 in which the ground and power contacts have been omitted;

Fig. 15 is a horizontal cross-sectional view through the cut away view in Fig. 14;

Fig. 16 is a computer generated representation of predicted stresses in an insulative housing similar to those illustrated in the preferred embodiments of the present invention;

Fig. 17 is a graph of contact retention force as a function of the amount of deformation (compression) in a rib of the insulative housing as is shown in Fig. 14.

Fig. 18 is a side cross sectional view in fragment of another embodiment of a connector according to the present invention.

Detailed Description of the Preferred Embodiments

[0026] Referring generally to Figs. 1 - 2 and 12 - 13, a set of intermating connectors according to a first embodiment of a high density connector of the present invention includes a receptacle which is shown generally at numeral 10. A base section of the receptacle is shown generally at numeral 12. The base is preferably formed by molding an appropriate insulating polymeric material capable of withstanding SMT reflow temperatures, for example, liquid crystal polymer (LCP). Referring first to the base section, this element includes a base wall 14 having an exterior side 16 and an interior side 18. On the exterior side there are outer recesses as, for example, recesses 20, 22, 24, 26 and 28 (Fig. 12). On the interior side there are inner contact receiving recesses as, for example, recesses 30, 32, 34, 36 and 38. Connecting these inner and outer recesses are medial slots as, for example, slots 40, 42, 44, 46 and 48. Each of the outer recesses has a base wall and a lateral wall as, for example, base wall 50 and lateral wall 52 (Fig. 12). Each of the inner signal contact receiving recesses has a base wall and intersecting lateral walls as, for example, base wall 54 and lateral walls 56 and 58. Each of the inner ground or power contact receiving recesses also has a base wall and diagonal lateral walls as, for example, base wall 60 and lateral walls 62 and 64. The above described inner and outer recesses and connecting medial slots receive ground/power contacts or signal contacts.

[0027] The ground or power contacts preferably have an upper section, shown generally at numeral 66, formed of two contacting forks 68 and 70. Each of these forks has a converging section 72, a contact point 74 and an outwardly diverging or lead-in section 76. The ground or power contacts also include a medial section 78 passing through the lower wall of the receptacle and a lower section 80 that extends into the outer recess. A solder ball 82 is fused onto lower section 80, as will be described below.

[0028] Each of the signal contacts (Figs. 12 and 13) includes an upper section shown generally at numeral 84 preferably having a contact projection 86, a lead-in bend 88 and a stiffening rib 90. The signal contacts also include a medial section 92 which passes through the lower wall of the receptacle. Each signal contact includes a lower section 98 (Fig. 13) extending into the outer recess for example, recess 22 in Figs. 12 -13, where a solder ball 100 is fused to lower section 98 as will be explained below.

[0029] Referring particularly to Figs. 1 - 2, the base section of the receptacle includes latching structures, for example, as is shown generally at numeral 102. This latching structure includes an upward tab 104 which is superimposed over a vertical groove 106 and which has an outward projection 108. The base section of the receptacle also has other similar latching structures 110, 112 and 114. The receptacle also includes an upper section shown generally at 116 which is superimposed over the base section. This upper section has a top wall 118 and a peripheral side wall 120. This upper section is fixed to the base section by means of latching structures as is, for example, shown generally at numeral 122. Each of these latching structures has a side wall recess 124 and a U-shaped latch 126 which extends downwardly from the top wall and is spaced from the side wall recess. The tab 104 fits between the U-shaped latch 126 and the side wall recess 124 to enable the U-shaped latch to engage the outward projection 108 on the latching structure 102 of the base section. The upper section includes other similar latching structures 128, 130 and 132 which engage, respectively, latching structures 110, 112 and 114 on the base section. The upper section 116 or the base 102 also may have mounting brackets 134 and 136 which have fastener apertures 138 and 140, respectively. On the top wall 118 of the upper section 116 there are also signal contact access apertures as, for example, apertures 142 and 144. These access apertures are arranged in a plurality of rows corresponding to the rows of signal contacts in the base section. Interposed between these rows of signal contact access apertures are elongated ground or power contact access slots as, for example, slots 146 and 148. The upper section 116 forms a mating interface between receptacle 10 and a mating plug 150 described below.

[0030] Referring to Figs. 3 - 4 and Fig. 11, the plug element of the connector is shown generally at numeral 150. The plug includes a base wall 152 and a peripheral side wall 154. There are opposed gaps 156 and 158 in the side wall and there is an open side 160 in opposed relation to the base wall. Projecting laterally from the plug are mounting brackets 162 and 164 having fastener receiving apertures 166 and 168 respectively, that are alignable with the fastener receiving apertures 138, 140 in the mounting brackets of the receptacle.

[0031] Referring to Fig. 11, on the inner side of the base wall 152 there are inner signal contact receiving recesses such as recess 170. Also on the inner side of the base wall are inner power or ground contact receiving recesses such as recess 172. In opposed relation to the outer recesses on the base wall there are outer signal contact receiving recesses such as recess 174, and outer power or ground contact receiving recesses, as at recess 176. Connecting the outer and inner signal contact receiving recesses and the outer and inner power or ground contact receiving recesses are, respectively, medial slots 178 and 180. Mounted in the power/ground contact receiving recesses via the medial slots 180 are power or ground contacts, shown generally at numeral 182. Each contact 182 has an elongated inner section 184, an elongated medial section 186, which is mounted in base wall 152, and an outer section 188 extending into recess 176. A solder ball 190 is fused onto section 188. The outer section 188 and the solder ball are partially contained in the outer recess 176. The plug also includes a plurality of signal contacts 192. These signal contacts each have an inner section 194, a medial section 196 mounted in the base wall, and a terminal tab 198 extending into recess 174. A solder ball 200 is fused onto terminal tab 198. Again it will be observed that this outer section and the solder ball are partially contained in the outer recess as at 170.

[0032] Referring to Figs. 5 - 7c, it will be seen that the plug described above is mounted on a circuit substrate, such as a rigid PWB 202, and the receptacle is mounted on a similar PWB 204. The plug and receptacle thereby form a board to board interconnection, as illustrated in Fig. 6. The plug has a two dimensional array of signal contacts, such as 192 onto which are fused solder balls 200 and a plurality of ground/power contacts, such as contacts 192, onto which are fused solder balls 190. By use of SMT techniques, the solder balls are also fused to the PWB 202 to fix the entire plug to the PWB and effect electrical contact between the signal contacts and ground or power contacts in the plug and the PWB. It will be appreciated that although not all contacts are illustrated in Fig. 5, all such contacts are connected to solder balls and to the PWB in the same way. Similarly, solder balls 100 are fused onto receptacle signal contacts 84 and those solder balls are fused to the PWB 204. Receptacle ground/power contacts 66 are mounted in slot 134 and are fused to solder balls 82 and these solder balls are fused to PWB 204.

[0033] The plug is aligned with the receptacle so that the peripheral side wall 154 of the plug overlaps the peripheral side wall 120 of the upper section 118 of the receptacle.

[0034] Referring particularly to Figs. 7a - 7c the engagement of the plug and receptacle is shown in greater detail. Fig. 7a shows, after initial alignment, the ground/power contacts in the plug initially entering the ground/power contact receiving slots in the receptacle and engaging the corresponding power/ground contacts in the receptacle. The signal contacts have entered the signal contact slots in the receptacle. Fig. 7b shows the signal contacts in the plug initially engaging the corresponding signal contacts in the receptacle and the power/ground contacts in the plug becoming further engaged between the opposed leaves of the power ground contacts in the receptacle. Fig. 7c shows that the signal contacts in the plug being fully engaged with the signal contacts in the receptacle. The power/ground contacts in the plug have become positioned at the base of the fork of the power/ground contacts in the receptacle.

[0035] Referring to Fig. 8, the exterior side 16 of the base section 12 of the receptacle is shown prior to the application of the solder balls. Prior to the application of the solder balls, the terminal tabs of the signal contacts, for example, terminal tab 82, and of the power ground contacts, for example terminal tab 98, are disposed within a corresponding outer recesses for example, outer recesses 20, 22, 24, 26 and 28, by insertion of the contacts into the opposite surface 18 of the base 12. A quantity of solder paste of appropriate composition is applied to substantially fill each outer recess. The solder balls are then applied over the outer or mounting surface of the base. Preferably, the outer recesses are smaller in transverse extent than the solder balls, so that the solder balls are supported on the edges of the recesses, at a position near the terminal tabs of the contacts. To maximize the stability of the solder ball in the recess, a recess that is round or the shape of a regular polygon in cross-section is preferred. The solder paste aids in holding a solder ball in each of the exposed recesses as is shown in Fig. 9, where, for example, solder ball 82 is shown in recess 20 and solder ball 100 is shown in recess 22. Additional solder balls, 230, 232 and 234 are shown, for example, in recesses 24, 26 and 28. A solder ball will be positioned in all of the outer recesses of the receptacle. It will also be understood that the exterior side of plug will be substantially identical to the exterior side of the receptacle before placement of the solder balls as is shown in Fig. 8 and after emplacement of the solder balls as is shown in Fig. 11. After emplacement of the solder balls in the outer recesses, the connector is subjected to a reflow process to fuse the solder balls onto the terminal tabs. The exterior sides of the connectors, together with the solder balls and particularly the outer surfaces of the solder balls, form a substantially planar mounting interface, along which the connector is mounted onto a supporting circuit substrate, such as a PWB.

[0036] Figures 10 and 13 show a variant of the Figure 1 embodiment wherein, instead of the forked receptacle contacts 66, oppositely disposed pairs 66a and 66b of blade type contacts engage the ground/power terminals 182.

[0037] As previously mentioned, components such as electrical connectors, that are to be mounted on circuit substrates by SMT techniques must meet very demanding specifications for coplanarity. If tight tolerances on coplanarity, usually on the order of about 0.08 to about 0.1 mm (0.003 to about 0.004 inch), are not maintained, manufacturers experience undesirably high failure rates resulting from faulty solder connections. Variations in the distance of a surface mount portion of a contact from the circuit substrate can result from variations in the location of the contact in the insulative housing occurring as a result of the contact insertion process and from deformation of the housings, resulting in bowing or warping of the mounting interface of the connector body. Connectors made in accordance with the present invention are capable of attaining strict coplanarity requirements by use of features that carefully locate and size the fusible bodies used for bonding the connector to a substrate and by the use of contact securing arrangements that prevent accumulations of stresses in the connector housing that tend to distort the housing.

[0038] In the embodiments of Figures 1 - 13 the metal contacts are secured in insulative housings in a manner to avoid the inducing of stress in the body of the housing. This securing is achieved by the use of a shaped slot or opening into which a securing portion of the contact is inserted. In one arrangement especially useful for the smaller signal contacts, the slot has a shape that closely conforms in shape and dimensions to all the surfaces of the contact but one. The wall of the slot facing that one surface has an integrally molded lateral projection projecting into the slot. The distance between the distal end of the projection and the opposing wall of the slot is less than the thickness of the contact. Thus the distal portion of the projection is engaged by and deformed by the contact as it is inserted into the slot. The contact is held securely in the slot by the normal force exerted on the contact by the deformable projection. Because the distal of the projection is free to deform, the build up of stresses in the housing is avoided. In the preferred embodiments illustrated, the projection comprises a pyramidal rib integrally formed on one of the side walls of the slot.

[0039] The specific rib configuration illustrated is believed to be optimum for the particular housings in which it is employed, but other similar ribs of somewhat different shape or size might be advantageously employed with other types of housings. Referring particularly to Figs. 14 and 15, a signal contact 494 is retained in slot 496 and abuts against rib 498. The rib has a planar surface 500, where it engages the contact 494, and opposed oblique sides 502 and 504. The contact 494 is securely retained in the slot by engagement with the back and side edges of the slot 496 and rib 498. The portion of the rib adjacent surface 500 is free to deform as contact 494 is forced into slot 496, thereby relieving any stresses that result from contact insertion.

[0040] Similarly, a power/ground contact is retained in slot 508 and bears against deformable rib 510. The rib has a distal portion 512, where it abuts against the contact, and opposed oblique sides 514 and 516. In this arrangement, there is also an opposed rib as, for example, rib 518. This opposed insulative rib also has a distal portion 520 and oblique sides 522 and 524. The opposed deformable ribs can be used for securing larger contacts and for centering the contact in the slot. Those skilled in the art will also appreciate the particular shape, size, number and placement of such ribs may vary for different types of housings, and these factors would be selected so that, to the greatest extent possible, stresses in the housing are isolated in the deformable ribs. Fig. 16 which was generated using ANSYS stress analysis software available from Ansys, Inc. of Houston, Pennsylvania shows that by use of the contact securing arrangement illustrated in Figs. 14 and 15, high levels of stress are essentially isolated in the ribs, and do not extend substantially beyond the contact mounting slots thereby significantly reducing the risk of warpage or twisting of the housing which could otherwise result from a large number of contact insertions. The units for the various stress areas shown in Fig. 16 is N/mm² and the mm is the unit for displacement shown. Fig. 17 shows that, for a typical contact 494, increases in deformation (compression) of the distal portion of the deformable rib up to about 0.01 mm (0.0004 inch) resulted in an increasing retention force between the contact and the housing, resulting from the normal force imparted on the contact by the rib. After 0.01 mm (0.0004 inch) of deformation (compression), only minor increases in retention force resulted.

[0041] As previously mentioned, another factor influencing coplanarity of the substrate mounting face of a connector utilizing BGA mounting is the uniformity of the size of the solder balls and the position of the solder balls with respect to the board mounting face of the connector housing. In the preferred embodiments previously described, the termination tab of each contact is positioned in a recess. The outer recesses are substantially uniform in size and shape. These recesses provide several features of importance with respect to the present invention. The recesses can receive a highly uniform amount of solder paste placed therein, for example, by a simple deposit and squeegee operation. Thus the amount of solder available for securing each solder ball onto a contact is substantially uniform. The recesses locate the position of each solder ball in the lateral X - Y directions prior to attachment of the solder balls onto the contacts. The recesses also locate the solder balls in the Z direction with respect to the bottom surface of the housing and the distance of the solder ball from the terminal tabs of the contacts. The nominal extension of the tab into the recess is set so that at the maximum of the tolerance for extension of the tab into the recess, the tab does not touch the solder ball and thereby influence its Z direction location. However, fusing of the solder ball onto the contact tab is assured by having a relatively uniform and adequate amount of solder, from the solder paste, in the recess. Any variation in the distance between the contact tab and the solder ball is absorbed by the variable volume of solder paste placed in the recess.

[0042] Referring to Fig. 18, an embodiment of the invention having another arrangement for affixing solder balls is shown. The receptacle of this connector is shown generally at numeral 324. This receptacle has a base wall 326 having an exterior side 328 and an interior side 330. On the exterior side there are recesses such as 334a. Each of these recesses preferably has an oblique base wall 360a having a rounded surface 362a. On the interior side 330 there are recesses 358. Between the exterior and interior recesses there are medial slots 374. Each of these slots has a retention projection (not shown) for retaining the contact in the slot, in a manner substantially the same as that previously discussed in connection with Figs. 14 and 15. On the interior side, the receptacle has substantially the same construction as the receptacle illustrated in Figs. 1 and 2. It includes an upper section 436 secured on base 326 in a suitable manner, preferably by latches (not shown) as discussed with respect to Figs. 1 and 2.
The signal contacts, such as contact 408, and ground/power contacts are of a form substantially as described with respect to any of the previous described embodiments. Each signal contact, such as contact 408, has an upper section 410 with a forward projection 412 and rearward bend 414. The signal contact also has a medial section 416 where it engages the insulative housing and a lower tab 418 located in recess 334a.

[0043] The tab 418 of signal contact 408 is formed by bending the tail portions of the respective terminals about the surfaces 362a, after the contacts are inserted into base 326. Each surface 362a serves as bending mandrel for an associated contact tail. The tails are bent to the extent of the oblique surface 360a and are allowed to spring back so that the tabs are transverse to the longitudinal axis of the contact and are substantially parallel to the surface 328a. This assures a high degree of coplanarity of the tabs. Subsequent to formation of the tabs, solder paste is applied to the outside surface of each tab. Solder balls, such as 398a are then applied to the tabs and the assembly is heated to fuse the solder paste and solder ball onto each tab. In the structure, shown in Fig. 18, the recess 334a is deepened so that surfaces 360a and 362a are positioned further from bottom surface 328a. As a result, the solder ball 398a is located partially within the recess 334a and is stabilized by the edges thereof, as previously discussed especially with respect to Figs. 12 and 13. As a result, when solder balls of highly uniform size are used, these arrangements can yield finished connectors that exhibit coplanarity of the contacts across the mounting interface.

[0044] In this invention the conductive element will preferably be a solder ball. Those skilled in the art, however, will appreciate that it may be possible to substitute other fusible materials which have a melting temperature less than the melting temperature of the insulative body. The fusible element can also have a shape other than a sphere. The solder ball or other conductive element will also preferably have a diameter which is from about 50 percent to 200 per cent of the width of the recess. This diameter will also preferably be related to the depth of the recess and be from 50 percent to 200 percent of that depth. The volume of the solder ball will preferably be from about 75 percent to about 150 percent of the volume of the recess and, more preferably, will be about the same volume as the recess. The contact tab will extend into the recess by a sufficient amount to present adequate surface area for the solder ball to fuse to, and will usually preferably extend into the recess from about 25 percent to 75 percent and more preferably to about 50 percent of the depth of the recess as previously mentioned. The recesses ordinarily will be circular, square or the shape of any other regular polygon in cross section. When the conductive element is solder, it will preferably be an alloy which is in the range of about 90%Sn and 10%Pb to about 55%Sn and 45%Pb. More preferably the alloy will be eutectic which is 63%Sn and 37%Pb and has a melting point of 183°C. Typically, a "hard" solder alloy with a higher lead content would be used for mating to materials such as ceramics. The "hard" solder ball will "mushroom" or deform slightly as it softens under typical SMT conditions, but will not melt. A "soft" eutectic ball is used for attachment to PCB's and will usually reflow and reform itself under typical SMT conditions. Other solders known to be suitable for electronic purposes are also believed to be acceptable for use Such solders include, without limitation, electronically acceptable tin-antimony, tin-silver and lead-silver alloys and indium. Before the solder ball or other conductive element is positioned in a recess, that recess would usually be filled with solder paste.

[0045] While it is believed that a solder paste or cream incorporating any conventional organic or inorganic solder flux may be adapted for use, a no clean solder paste or cream is preferred. Such solder pastes or creams would include a solder alloy in the form of a fine powder suspended in a suitable fluxing material. This powder will ordinarily be an alloy and not a mixture of constituents. The ratio of solder to flux will ordinarily be high and in the range of 80% - 95% by weight solder or approximately 80% by volume. A solder cream will be formed when the solder material is suspended in a rosin flux. Preferably the rosin flux will be a white rosin or a low activity rosin flux, although for various purposes activated or superactivated rosins may be used. A solder paste will be formed when a solder alloy in the form of a fine powder is suspended in an organic acid flux or an inorganic acid flux. Such organic acids may be selected from lactic, oleic, stearic, phthalic, citric or other similar acids. Such inorganic acids may be selected from hydrochloric, hydroflouric and orthophosphoric acid. Cream or paste may be applied by brushing, screening, or extruding onto the surface which may advantageously have been gradually preheated to ensure good wetting. Although it has been found that wicking of the solder onto the contact is significantly reduced when a solder paste or cream is used, it is believed that paste type solder flux alone may also be used when a suitable, passivation agent is used. Such a suitable passivation agents would include fluoride containing solder resist coatings such as FLOURAD which is available from the 3M Corporation.

[0046] Heating is preferably conducted in a panel infra red (IR) solder reflow conveyor oven. The solder element would ordinarily be heated to a temperature from about 183° to about 195° C. But, depending on the material of the housing, solders having melting temperatures may be used. The conveyor oven would preferably be operated at a rate of speed from about 254 to 356 mm (10 to 14 inch) per second and would be moved through a plurality of successive heating phases for a total time of about 5 minutes to about 10 minutes.

[0047] Prior to being inserted into the conveyor oven the connector housing, contacts and solder elements may be preheated at an elevated temperature for at least an hour. In the conveyor oven a temperature profile would be developed based on an appropriate peak temperature, maximum slope and time above reflow temperature. Peak temperature is the highest temperature reached by the housing. For a solder element with a melting point of 183°C, peak temperature would usually be between 185°C and 195°C. Maximum slope is measured in °C/sec and specifies how fast the connector housing temperature is allowed to change, so as to avoid warping or bending. For most applications method, maximum positive slope will preferably initially be from about 2°C/sec to 15°C/sec. After the wetting point of the solder is reached negative slope will preferably be -2°C/sec to -15°C/sec. An important aspect of this invention is that time above reflow is minimized. Time above reflow is a measure of how long the solder element remains in its liquid phase. It is found that when time of the solder in its liquid phase is minimized, wicking of solder from the recess up the contact is eliminated or significantly reduced. Preferably rise time of temperature as measured on the board between 180°C and 200°C and fall time of temperature as measured on the board between 200°C and 180°C will both be from about 10 seconds to about 100 seconds. While not intending to be bound by any particular theory, it is believed that during such relatively short periods of time, surface tension of the liquid solder element will restrain the liquid solder from flowing through the contact receiving slot in the base of the recess. After such periods of time, however, the liquid solder will begin to flow through the contact receiving slot and wick up the contact. Prior to bringing the temperature of the solder element to its melting temperature, it may also be advantageous to initially have a relatively high slope but before melting temperature is reached to slow the rate of temperature increase or decrease after which a relatively high slope is then adopted until the melting temperature is reached. The selection of an appropriate housing material may also enhance results. Preferably the housing material will be wholly aromatic liquid crystal polyester (LCP) with characteristics of high glass transition temperature, low thermal coefficient, low moisture absorption, high fracture toughness, good flow and low viscosity, high temperature and high flash point.

[0048] It will be appreciated that an electrical connector has been described in which the connector that can utilize BGA technologies for mounting on a PWB. Surprisingly and unexpectedly it was also found that there was a relatively high degree of uniformity in the profiles of the solder balls and, in particular, in the weights and/or volume of the solder balls.

[0049] While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Further, the arrangements described can be used with respect to components other than connectors, that comprise housings formed of insulative materials which carry elements to be fused onto a PWB or other electrical substrate.

[0050] Therefore, the present invention should not be limited to any single embodiment, but rather construed in scope of the appended claims.

Claims

1. An electrical high density connector to be mounted onto the surface of a substrate (202, 204) having a conductive element comprising:

a contact with a lower section (80, 98, 188), having a terminal tab, adapted to be electrically connected to said conductive element;

a base wall (12, 152) formed by an insulating polymeric material, the base wall having an interior side and an exterior side adapted to face the substrate;

an exterior element (82, 100) of fusible electrically conductive material disposed on the terminal tab, said element being adapted to provide the primary electrical current path between the connector and the substrate, wherein the basewall comprises a plurality of contact receiving inner passageways (20, 22, 24, 26, 28; 40, 42, 44, 46, 48; 30, 32, 34, 36, 38), each extending from the interior side of said base wall to said exterior side of said base wall, said contact is positioned in a respective one of said plurality of contact receiving inner passageways, and said exterior element (32, 100) of fusible, electrically conductive material extends at least partially into said respective one of said plurality of contact receiving inner passageways.

2. An electrical high density connector according to claim 1, characterized in that the exterior element (82, 190) is a solder ball.

3. An electrical high density connector according to claims 1 and 2, characterized in that the lower section and the solder ball are partially contained in the outer recess.

4. An electrical high density connector according to claims 1 to 3, characterized in that each solder ball being secured on one of the contacts forms a mounting interface for mounting the connector on the substrate.

5. An electrical high density connector according to claim 1, characterized in that in an opening with a side wall section, for receiving a section of a contact, a deformable member is located adjacent said side wall and adapted to be deformed by the said contact inserted into the opening and secure the contact in the opening.

Ansprüche

1. Steckverbinder hoher Kontaktdichter zur Montage auf der Oberfläche eines Substrats (202, 204) mit einem leitenden Element, mit:

einem Kontakt mit einem unteren Bereich (80, 98, 188) mit einer Kontaktfahne, zur elektrischen Verbindung mit dem leitenden Element;

einer Bodenwand (12, 152) aus einem isolierendem Polymermaterial, mit einer Innenseite und einer Außenseite, die gegenüber dem Substrat positionierbar ist;

einem äußeren Element (82, 100) aus schmelzbarem elektrisch leitendem Material, welches auf der Kontaktfahne angeordnet ist, wobei das Element einen primären elektrischen Strompfad zwischen dem Steckverbinder und dem Substrat herstellt, wobei die Bodenwand eine Mehrzahl kontaktaufnehmender innerer Durchgangspassagen (20, 22, 24, 26, 28; 40, 42, 44, 46, 48; 30, 32, 34, 36, 38) aufweist, die sich jeweils von der Innenseite der Bodenwand aus zur Außenseite der Bodenwand erstrecken und wobei der Kontakt jeweils in einem der Mehrzahl von inneren Kontaktaufnahmedurchgangspassagen angeordnet ist und das äußere Element (32, 100) aus schmelzbarem elektrisch leitenden Material sich zumindest teilweise jeweils in eins der Mehrzahl der kontaktaufnehmenden inneren Durchgangspassagen erstreckt.

2. Steckverbinder hoher Kontaktdichte nach Anspruch 1, dadurch gekennzeichnet, dass das äußere Element (82, 190) eine Lötzinnkugel ist.

3. Steckverbinder hoher Kontaktdichte nach Anspruch 1 und 2, dadurch gekennzeichnet, dass der untere Bereich und die Lötzinnkugel teilweise im äußeren Schlitz angeordnet sind.

4. Steckverbinder hoher Kontaktdichte nach den Ansprüchen 1 bis 3, dadurch gekennzeichnet, dass jede Lötzinnkugel an einem der Kontakt befestigt und eine Montagefläche zur Montage des Steckverbinders am Substrat darstellt.

5. Steckverbinder hoher Kontaktdichte nach Anspruch 1, dadurch gekennzeichnet, dass in einer Öffnung mit einem Seitenwandbereich zur Aufnahme eines Bereichs eines Kontakts ein verformbares Glied benachbart zur Seitenwand angeordnet ist, welches durch den in die Öffnung eingeführten Kontakt verformbar ist und den Kontakt in der Öffnung haltert.

Revendications

1. Connecteur électrique à haute densité devant être monté sur la surface d'un substrat (202, 204) ayant un élément conducteur comprenant :

un contact avec une section inférieure (80, 98, 188), ayant une languette terminale, adaptée pour être connectée électriquement audit élément conducteur ;

une paroi de base (12, 152) formée par un matériau polymère isolant, la paroi de base ayant un côté intérieur et un côté extérieur adaptés pour faire face au substrat ;

un élément extérieur (82, 100) en matériau fusible électriquement conducteur disposé sur la languette terminale, ledit élément étant adapté pour assurer le trajet du courant électrique principal entre le connecteur et le substrat, dans lequel la paroi de base comprend une pluralité de passages internes de réception de contacts (20, 22, 24, 26, 28 ; 40, 42, 44, 46, 48 ; 30, 32, 34, 36, 38), chacun s'étendant à partir du côté intérieur de ladite paroi de base au côté extérieur de ladite paroi de base, ledit contact est positionné dans un passage respectif desdits passages internes de réception de contacts, et ledit élément extérieur (32, 100) en matériau fusible électriquement conducteur s'étend au moins partiellement dans ledit passage respectif de ladite pluralité de passages internes de réception de contacts.

2. Connecteur électrique à haute densité selon la revendication 1, caractérisé en ce que l'élément extérieur (82, 190) est une bille de soudure.

3. Connecteur électrique à haute densité selon les revendications 1 et 2, caractérisé en ce que la section inférieure et la bille de soudure sont partiellement contenues dans l'évidement externe.

4. Connecteur électrique à haute densité selon les revendications 1 à 3, caractérisé en ce que chaque bille de soudure étant fixée sur un des contacts forme une interface de montage pour monter le connecteur sur le substrat.

5. Connecteur électrique à haute densité selon la revendication 1, caractérisé en ce que dans une ouverture avec une section de paroi latérale, pour recevoir une section d'un contact, un élément déformable est situé près de ladite paroi latérale et est adapté pour être déformé par ledit contact inséré dans l'ouverture et fixer le contact dans l'ouverture.

Drawing